1. Field of the Invention
The invention relates to a method for preparing nano-crystalline TiO2 thin films, and to environmental applications, particularly to the use of the nano-TiO2 thin films under ultraviolet irradiation in killing bacteria and viruses in the environment.
2. Description of the Related Art
It is always a challenge to remove organic pollutants in air and to kill the bacteria and viruses in the environment in the fields of environmental science and medicine. In modern society, various organic pollutants and a great number of bacteria and viruses fill the crowded offices, shopping malls and public places. The health of people who live and work under such environments will obviously be affected.
It is known that TiO2 semiconductors can effectively decompose organic pollutants in air and water under ultraviolet and kill bacteria therein. Therefore, a simple and feasible way is to have nano-crystalline TiO2 immobilized on the surface of a substrate such as glass, metals and constructive materials, and then expose the substrate under ultraviolet to catalytically kill bacteria.
There have been many processes disclosed to fix TiO2 to the substrate of glass, metals and ceramics, such as chemical vapor deposition, magnetic spraying, high speed spinning coating and pyrolysis. TiO2 thin films prepared by these processes exhibit very poor photocatalytic and antibacterial activities or are easy to peel off from the substrate for the reasons that the TiO2 thin films have poor crystallinity (even non-crystalline), and poor adhesivity with substrates to which they attach.
Chinese patent application No. 01128306.8 filed on Jul. 31, 2001 and published as CN 1400186A, on Mar. 5, 2003. As such, this patent application is not believed to qualify as prior art to the present application which has a priority date of Oct. 28, 2002. The application discloses a process for improving photocatalytic activities of TiO2 thin films on glass. The process includes preparing a sol gel of TiO2, coating the thin film on glass, treating the thin film using an acid, washing the treated thin film, and drying the thin film. The sol-gel is prepared by hydrolysis of titanium alkoxide. A stabilizer selected from triethanolamine, diethanolamine etc is used in preparation of the sol-gel.
Chinese patent application No. 01130896.6 filed on Aug. 31, 2001 and published on Apr. 3, 2002, discloses a process for preparing photo-catalysts of Meso-TiO2 thin films. The process includes preparing a sol gel solution that is made from a titanium alkoxide or a titanium chloride, lower alkanol diethanolamine, water and polyethylene glycol having a molecular weight from 200 to 4,000; coating a thin film on a substrate by spinning coating or dip coating; and drying and calcining the thin film.
Chinese patent application No. 0110064.8 filed on Mar. 29, 2001 and published on Sep. 12, 2001, discloses a process for preparing a thin film of TiO2 on a substrate. The process includes stirring a solution consisting of titanium alkoxide, ethanol amines and ethanol; adding to the solution a fluorine-containing compound or an aqueous solution of transitional metals, and coating a thin film on the substrate.
It is known that photocatalytic and antibacterial activities, and hydrophilicity of a TiO2 thin film are significantly influenced by its phase constitutions, specific surface area, and porous size and distribution. It is understood that the above parameters of a TiO2 thin film are affected by the process for preparing the same. Therefore, the process for preparing a thin film will significantly affect the photocatalytic activity of the TiO2 thin film. The inventors, after conducting careful investigations, have found out that the reverse micelle technique is an effective method for preparing TiO2 thin films with high photocatalytic activities. Moreover, a thin film prepared by the reverse micelle solution shows higher photocatalytic activity than those prepared by other processes in the prior art. The present invention is hereby provided. The TiO2 thin film provided by the present invention is suitably used to photocatalytically decompose organic pollutants in air and thereby to kill bacteria and viruses in an environment.